xp won't run after malwarebytes was ran

Welcome to Major Geeks!

Sounds like you had an infection that may have caused one of your necessary Windows system files to be removed or it was corrupted. You did not say what version of Windows you are running so I will assume it is Windows XP. Do you have you Windows XP boot CD? If so, you should boot to the Recovery Console and check to see if the C:\Windows\system32\drivers\atapi.sys file exists. If this file was deleted, you would have the problem you described. You can just enter the below command at the Recovery Console prompt to look for the file:

dir c:\windows\system32\drivers\atapi.sys


See if it finds the file or not. This is just the first step. We need to see if it exists and if not, we need to replace it by copying the file from another location.


If you don't know how to boot to the Recovery Console, see this: http://support.microsoft.com/kb/314058

 

First let's find out the answer to a couple other questions.

1. Are there any error messages at all while trying to boot up? Anything about missing files? If so what messages exactly?
2. Have you tried booting to Last Known Good Configuration?
3. Have you tried booting in Safe Mode?
4. How about Safe Mode with Command Prompt?

If none of the above other boot mode works, you will have to try using Microsoofts procedure documented in the below to restore a registry hive from a point in time before the problem began (i.e., before running Malwarebytes or even from before the infection)

http://support.microsoft.com/default.aspx?scid=kb;en-us;307545&sd=tech